Doped ammonium perchlorate oxidizers and method of preparing same

ABSTRACT

AN IMPROVED CLASS OF OXIDIZERS IS FORMED BY PRECIPITATING CRYSTALS FROM AN ACID SOLUTION IN WHICH AMMONIUM PERCHLORATE HAS BEEN DISSOLVED AND FROM AN ACID SOLUTION IN WHICH AMMONIUM PERCHLORATE AND AQUANTITY OF INTRONIUM PERCHLORATE HAVE BEEN DISSOLVED.

United States Patent C ABSTRACT OF THE DISCLOSURE An improved class ofoxidizers is formed by precipitating crystals from an acid solution inwhich ammonium perchlorate has been dissolved and from an acid solutionin which ammonium perchlorate and a quantity of nitronium perchloratehave been dissolved.

One important use of oxidizersis supplying oxygen to fuels in solidpropellant compositions and ammonium perchlorate (AP) is a cornmo nlyused propellant oxidizer.

An increase in the burning rate of ammonium perchlorate accelerates therelease of oxygen to the fuel. Numerous methods for enhancing ammoniumperchlorate burning rate have been developed. In some of these,additives are mixed with the AP on a macroscopic level.

However, it is usually important that oxidizers burn uniformly, and onedisadvantage of additives that have been mechanically mixed intooxidizers in the prior art has been that the inhomogeneity of themixture often resulted in uneven burning. Also, solid bi-propellants areoften made'by mixing an oxidizer with a fuel and a binder, andmechanically mixed accelerators are sometimes not compatible with thebinder material.

More recently, varieties of AP with accelerated burning rates have beendeveloped that avoid both of the above enumerated problems byincorporating particular accelerating additives into the AP crystalstructure. This invention provides improved AP oxidizers of the lattertype, where the oxidizer crystals comprise AP doped with additives.

It is an object of this invention to provide an AP oxidizer that burnsfaster than pure AP.

Another object of this invention is to provide an AP base oxidizer inwhich one or more additives are incorbase porated into the crystalstructure, the homogeneous distribution thus eifected providing veryuniform burning and preventing undesirable reactions with bindermaterials.

A further object of this invention is to provide an AP base oxidizerwith an accelerated burning rate that may be easily produced.

solved in nitric acid solutions of varying strengths. Crystalsprecipitated from these solutions are found to burn more rapidly thanpure AP crystals. Even precipitates from very weak nitric acid solutionsexhibit accelerated thermal decomposition compared to pure AP, althoughthe increase becomes less pronounced as the strength of the nitric acidsolution goes below about 20%. This is a gradual effect, however; thereis no sharp break point at the 20% solution level, nor is there anycritical lower level in solution percentage below which the effect isnot apparent. In the crystals precipitated from solution in thisembodiment, ions from the nitric acid are incorporated in the crystalstructure. It is believed that some of the ammonium ions are replaced inthe lattice by H+ ions and that some of the perchlorate ions arereplaced by N0 10118.

In still another inventive embodiment, AP is dissolved in hydrochloricacid solutions of varying strengths. Crystals precipitated from thesesolutions are found to burn significantly more rapidly than pure AP,although the increase is not as great as obtained from the two previousembodiments. Here again, ions from the acid solvent are incorporatedinto the crystal structure and it is believed that some ammonium andsome perchlorate ions are replaced in the crystal lattice by H+ andClions respectively.

In order that those skilled in the art may practice the invention, theexamples below set forth the details of the methods whereby oxidizers ofthis invention are prepared.

EXAMPLE I Ammonium perchlorate (AP) doped with nitronium perchlorate(NP) at 10- mole percent was prepared by placing 100 grams of analyticalgrade AP and 12.5 milligrams of analytical grade NP in 100% fumingnitric acid.

1 The solution was then heated to a temperature slightly In oneembodiment of this invention, an improved oximonium ions (NHJ) have beenreplaced in the crystal lattice with nitronium ions (NO from the NP,that other ammonium ions have been replaced with H+ ions from the nitricacid, and that some of the perchlorate ions (ClOr) have been replaced inthe lattice with NO; ions from the nitric acid. The crystals thusproduced burn much more rapidly than do pure 'AP crystals and alsoexhibit greater sensitivity to shock than either AF or NP. It isbelieved that the foreign ions incorporated into the crystal structureelfect the increase.

In another embodiment of the invention, AP is disbelow C. and stirreduntil the AP and NP were completely dissolved. The solution was thenallowed to cool to room temperature and the crystals that precipitatedwere filtered off and dried under vacuum for four days. The driedcrystals were then ground to a uniform particle size with an agatemortar and pestle. Strand burning tesls were then conducted with theground crystals thus obtained. Twelve 2-inch lengths of commercialstraws having a 4 mm. inside diameter were packed with the ground vcrystals, and four packed straws were burned at each of three pressureambients: 500 p.s.i.a., 1000 p.s.i.a. and 1500 p.s.i.a. The averageburning rates for the four samples at each pressure are given in TableI.

They provide a comparison; pure AP was burned. Ten straws, identical tothose used for the AP-NP material, were packed with analytical grade APof substantially the same particle size as that of the AP-NP materialand burned at 1000 p.s.i.a. The average burning rate of the ten APsamples is given in Table I. Also given in Table I are burning rates forpure AP at 500 p.s.i.a. and 1500 p.s.i.a. ambients, calculated from theexperimentally obtained 1000 p.s.i.a value by a curve found applicablein pervious tests on AP burning rates, as indicated in the footnotebeneath the table.

TABLE I Burning rate, inches/sec.

1 Calculated, using the measured rate at 1,000 p.s.i.a. and assuming astraight line log-log plot of burning rate vs. pressure with a slope of0.65 as has been found applicable in prior testing of AP burning rates.

The results given in Table I indicate that AP doped with NP andprecipitated out of a 100% nitric acid 'solii tion burns at asignificantly greater rate than pure AP at each of the three pressures.

The shock sensitivity of AP doped with NP in accordance with the methoddescribed in this example was obtained using a falling ball (modifiedJPL) type apparatus. The maximum energy that could be imparted by impactfor ten successive trials without visible reaction or decomposition was41.4 inch-lbs. When compared with shock sensitivity figures of greaterthan 100 inch-lbs. for AP and about 75 inch-lbs. for NP, it is apparentthat the AP-NP material is much more sensitive to shock than either pureAP or pure NP.

EXAMPLE II TABLE II Burning rate, inches/sec.

HNOs Pressure, p.s.i.a; doped AP AP 1 Calculated, using the measuredrate at; 1,000 p.s.i.a. and assuming a straight line log-log plot ofburning rate vs. pressure with a slope of 0.65 as has been foundapplicable in prior testing of AP burning rates.

It will be seen from Table II that the crystalline precipitate obtainedfrom dissolving AP in 100% nitric acid burns at a significantly morerapid rate than does pure AP.

EXAMPLE III Analytical grade AP was dissolved in different percentagesolutions of nitric acid and precipitate crystals obtained and preparedin accordance with the procedure described in Example H. Also, forcomparison, crystals were precipitated from AP dissolved in water withno nitric acid. For the latter, and for the various solutions containingless than 100% nitric acid, double distilled, de-ionized water was used.The thermal decomposition of the ground crystals so obtained wasmeasured by means of thermogravimetric (TGA) analysis of samples offifteen grams each in a dry helium atmosphere with a heating rate of 6C. per minute. The results are given in Table III.

TABLE TIL-PERCENTAGEgEiIGHT LOSS MEASURED BY Temperature 0.)

The results shown in Table III indicate that the crystals obtained bydissolving AP even in very weak solutions of nitric acid have asignificantly higher rate of thermal decomposition than does pure APprecipitated from water. These results are completely consistent withthe burning rate data of Table II, as indicated by the results of thezero and HNO data.

EXAMPLE IV TABLE IV.PERCENTAGE WGEgGHT LOSS MEASURED BY Temperature 0.)

Percent H01 290 330 390 A comparison of the data in Table IV with datain Table III indicates that crystals precipitated from solutions ofhydrochloric acid do not thermally decompose as rapidly as crystalsprecipitated from solutions of the same percentage of nitric acid,although they decompose significantly faster than AP crystalsprecipitated from water.

Various modifications of the above illustrative embodiments as willoccur to those skilled in the art are within the scope of the invention,which is defined solely by the appended claims.

What is claimed is:

'1. A method for producing an oxidizer having an enhanced rate ofthermal decomposition comprising dissolving ammonium perchlorate in anacid solution containing up to 100% of an inorganic acid and subsequent-1y precipitating crystals therefrom.

2. A method for producing an oxidizer having an enhanced rate of thermaldecomposition comprising dissolving ammonium perchlorate in an acidsolution containing up to 100% nitric acid and subsequentlyprecipitating crystals therefrom.

3. A method for producing an oxidizer having an enhanced rate of thermaldecomposition comprising dissolving ammonium perchlorate and nitroniumperchlorate in an acid solution and subsequently precipitating crystalstherefrom.

4. A method for producing an oxidizer having an enhanced rate of thermaldecomposition comprising dissolving ammonium perchlorate and nitroniumperchlorate in an acid solution containing up to 100% nitric acid andsubsequently precipitating crystals therefrom.

5. A method for producing an oxidizer having an enhanced rate of thermaldecomposition comprising dissolving ammonium perchlorate in an acidsolution containing up to 100% hydrochloric acid and subsequentlyprecipitating crystals therefrom.

6. An improved oxidizer comprising ammonium perchlorate in which H+ andN0 ions have been incorporated into the crystal lattice.

7. An improved oxidizer comprising ammonium perchlorate in which H NOand NO;;- ions have been incorporated into the crystal lattice.

8. An improved oxidizer comprising ammonium perchlorate in which H+ andClions have been incorporated into the crystal lattice.

(References I on following page) 5 References Cited UNITED STATESPATENTS Pino 149-74 Markowitz 2385 McCrone 149-76 Markowitz 14976Robinson 149-74 Lofiberg 14976 Stammler et a1. 14976 6 3,373,063 3/1968Bieber et a1 14974 3,383,180 5/1968 Kralik et a1. 23301 BENJAMIN R.PADGETI, Primary Examiner 5 S. I. LECHERT, JR., Assistant Examiner US.Cl. X.R.

